Process of preparing 6-methyl pteridines



Patented Nov. 23, 1948 PROCESS 0F- PREPAR-ING B-METHYL PTERIDINES .James H. Boothe, Pearl River, N. Y., assignor .to

American Gyanamid Company,

New York,

N. Y., a corporation of.Maine .No Drawing. Application Julyz'l, 1946., Serial No. 686,717

QGlaims. 1

This invention relates to a new method of preparing 2-amino-4-hydroxy=6-methyl 'pyrimido [4,5- bl pyrazine.

In the copending application of John H. Mowat, Serial No. 633,870, filed December 8, 1945,, now Patent ;No. 2,443,078, dated June 8, 1948. there is disclosed the preparation of certain 6- and "'1- alkyl substituted pyrimidopyrazines, including 2- amino-4-hydroxy-6 methyl pyrimido '[4,5-'bl pyrazine. This latter compound has proven to be useful in the production of Synthetic folic acid,

in which Y is a radical of the group consisting of the residue of tertiary amines, suchas CzHs and quaternary ammonium compounds. such as The preparation of preferred compounds of this class are shown in the specific examples.

To prepare the G-methyl pterins of the present invention the compounds of the Hultquist application are treated with a reducing agent, preferably metallic zinc and an alkali, whereby the group represented by Y in the general formula is split off and replaced with hydrogen. During this reduction the pyrazyl rin is in part hydrogenated to the dihydro form, but this product may be easily oxidized by treatment with oxidizing agents or even upon exposure to atmospheric oxygen to the desired compound of the present invention.

To illustrate the process in greater particularity the following examples disclose specific methods of preparing a preferred intermediate, followed 2 by "the reduction of compound toproduce the 6-methylypterin :of the present invention.

Example 1 To a solution of 15 gm. (0.07 mole) 2.4;5-triamino-G-hydroxy pyrimidine dihydrochloride in 200 cc. water was added enough pyridine to bring the solution to pH about 5. Tothis was added a solution of 21.4 gm. (0.1 mole) 2,3-dibromopropionaldehyde in cc. acetone, while adding pyridine as necessary to keep the mixture at pH 4-5 with cooling to keep the-temperature of the solution at 30-.-40 C. .As soon as no more pyridine was required to maintain the pH at 4-5, 20--gm. I-Iyflo was added, and a brown insoluble precipitate was filtered off and discarded. The filtrate was acidified with hydrochloric acid to pH .3-4, and .a solution of iodine in potassium iodide and water was added until the reaction mixture gave abide-black spot on starch-iodide .test paper. There was an immediate precipitation of the light tan crystalline N-[:(2-amino-4-hydroxy-6 -pyrimido [4,5-b] pyrazyl) methyl] pyridinium iodide amounting to 81gms. or 30% of theory.

1 gm. of the foregoing product was dissolved in 100 cc. of 1 N NaOH after which 3 gm. of zinc "dust was added and the mixture stirred for 30 minutes at room temperature. Theodor of pyridine wasqu'ite evident. The solution was filtered free of zinc and acidified to about pH 2. The precipitate which formed "was filtered out and dried. It weighed 035 A solution of 200 mg. of the above product in 10-15 cc. of dilute NaOH was treated with 3.74 cc. of 0.1 N KMnOr, dropwise'with stirring. This is the calculated amount of KMI104 to oxidizethe dihydro pteridine to the aromatic form. The 'KMnOI. was used up quite rapidly at room temperature. The resulting MnOz was filtered out and the solution acidified to pH "2 whereupon a precipitate was formed. The precipitated product, which was foundto be 2-amino-4-hydroxy-6- methyl pyrimido [4,5-bl pyrazine, was centrifuged and crystallizedas the sodium salt from 12 cc. of 5 N NaOH. The sodium salt "was dissolved in water and precipitated as the free acid by acidification. Further examination of the product proved itto be identicalwith a sample "[4,5-blpyrazyl) methyl] pyridinium iodide was dissolved in 1500 ml. 1N NaOH, stirred well and 45 g. zinc dust was added. After 30 minutes the zinc dust was filtered out and solid CO2 was added to precipitate the pteridine and ZnCOs. The precipitate was filtered off and then stirred with water and acetic acid added to pH 4 to dissolve out most of the ZnCOs. The residue was mixed with 500 ml. water and 200 ml. acetic acid which dissolved most of it. The solution was filtered and 56 ml. 30% H202 was added which oxidized the dihydro pteridine to the unsaturated 2-amino- 4-hydroxy-6-methyl pyrimido [4,5-b] pyrazine which immediately precipitated.

Exampl 3 product, 2-amino-4-hydroxy-S-methyl pyrimido [4,5-b] pyrazine, was filtered off. 7 It was crystallized from 250 ml. N NaOH as the sodium salt and then precipitated as the free acid.

Example 4 100 g. (2-amino-4-hydroxy-6-pyrimido [4,5-10] pyrazyl) methyl pyridinium iodide was dissolved in 4 liters of water containing 160 g. NaOH. 100

zinc dust was added and the mixture was stirred for minutes. The Zinc dust was filtered out and 16 ml. H202 was added. The solution was heated on a steam bath and clarified with charcoal. This solution was then added dropwise to a hot solution of 600 ml, acetic acid in 2 liters of water. After cooling, the product, 2-amino4-hydroxy-6-methyl pyrimido [4, 5-bl pyrazine, was filtered out and dried.

Example 5 To a solution of 216 gms (1 mole) 2,3-dibromopropionaldehyde in 500 cc. anhydrous ethercooled to 50 C. was added a solution at 50 C. of '73 gm. (1 mole) diethylamine in 500 cc. anhydrous ether with cooling to keep the temperature at -30 to 40 C. The slurry of white solid in ether was allowed to stand for an hour, during which time the temperature rose to +10 C. There was added 100 cc. water to dissolve the product, and the ether layer was discarded.

The water solution was added to 100 gm. (0.47 mole) 2,4,5triamino6-hydroxypyrimidine dihydrochloride suspended in 300 cc. water. Sodium hydroxide (5 N) was added to bring the pH to about 3, and 100 cc. solution containing 20 gm. iodine and 40 gms. potassium was added.

Concentrated sulfuric acid to pH 1-2 was added and the solution cooled to 30 C. The unreacted 2,4;5-triamino-Ghydroxypyrimidium sulfate was removed.

from 10% potassium iodide solution there was obtained bright yellow crystals of Z-aminoi-hy- 4 droxy-6-(diethylaminomethyl) pyrimido [4,5-bl pyrazine hydriodide.

A sample slurried in water and treated with sodium hydroxide to pH 8-8.5 gave a light-tan product, the analysis of which agreed well for that of 2-amino-4-hydroxy-6-(diethylaminomethyl) pyrimido [4,5-b] pyrazine.

Treatment of the above product with metallic zinc and an alkali as in the preceding examples results in the formation of 2-amino-4-hydroxy- 6-methyl pyrimido [4,5-bl pyrazine.

I claim:

1. A method of preparing 2-amino-4-hydroxy- 6-methyl pyrimido [4,5-b] pyrazine which comprises treating a 2-amino-4-hydroxy pyrimido [4,5-b] pyrazine having as a substituent at the 6-position the group CI-IzY in which Y is a nitrogen atom having additional substituents of the group consisting of those constituting tertiary amines and quaternary ammonium compounds with a reducing agent comprising metallic zinc and an alkali whereby the group represented by Y is removed and replaced with hydrogen and thereafter recovering Z-amino-l-hydroxy-fi-methylpyrimido [4,5-b] pyrazine.

2. A method of preparing 2-amino-4-hydroxy- G-methyl pyrimido [4,5-bl pyrazine which comprises treating an N-[(Z-amino--hydroxy-G-pyrimido [4,5-bl pyrazyl) methyl] pyridinium halide with metallic zinc and an alkali whereby the pyridinium halide group is removed and replaced with hydrogen and thereafter recovering Z-amino-4-hydroxy-G-methylpyrimido [4,5-10] pyrazine.

3. A method of preparing 2-amino-4-hydroxy- G-methyl pyrimido [4,5-b] pyrazine which comprises treating an N-E(2-amino-4-hydroxy-6-pyrimido [4,5-b] pyrazyl) methyl] pyridinium halide with metallic zinc and sodium hydroxide whereby the pyridinium halide group is removed and replaced with hydrogen and. thereafter recovering 2-amino4 hydroxy-B-methylpyrimido [4,5-b] pyrazine.

4. A method of preparing Z-amino--hydroxy- G-methyl pyrimido [4,5-b] pyrazine which comprises treating an N-[(2-amino-4-hydroxy-6-pyrimido [4,5-b] pyrazyl) methyl] pyridinium iodide with metallic zinc and sodium hydroxide whereby the pyridinium iodide group is removed and replaced with hydrogen and thereafter recovering 2-amino-4hydroxy-6-methylpyrimido pyrazine.

5. A method of preparing 2-amino-4-hydroxy 6-methyl pyrimido [4,5-bl pyrazine which comprises treating an N-l(2-amino-4-hydroxy-6-pyrimido [4,5-bl pyrazyl) methyl] pyridiniurn bromide with metallic zinc and sodium hydroxide whereby the pyridinium bromide group is removed and replaced with hydrogen and thereafter recovering 2-arnino-4-hydroxy-6methylpyrimido [4,5-b] pyrazine.

6. A method of preparingz-aminol-hydroxy- G-methyl pyrimido [4,5-bl pyrazine which comprises treating 2-amino-4-hydroxy-6-(dialkylamino-methyl) pyrimido [4,5-b] pyrazine with metallic zinc and sodium hydroxide whereby the dialkylamino group is removed and replaced with hydrogen and thereafter recovering 2-amino-4- hydroxy-G-methylpyrimido [4,5-b] pyrazine.

7. A method of preparing Z-amino-A-hydroxy B-methyl pyrimido [4,5-b] pyrazine which comprises treating 2-amino-4-hydroxy-6-(diethylaminomethyl) pyrimido [4,5-b] p razin with metallic zinc and sodium hydroxide whereby the diethylamino group is removed and replaced with hydrogen and thereafter recovering 2-amino-4- hydroxy-G-methylpyrimido [4,5-b] pyrazine.

8. A method of preparing 2-amino-4-hydroxy- G-methyl pyrimido [4,5-b pyrazine which comprises treating a 2-amino-4-hydroxy pyrimido [4,540] pyrazine having as a substituent at the 6-position the group -CH2Y in which Y is a nitrogen atom having additional substituents of the group consisting of those constituting tertiary amines and quaternary ammonium compounds with a reducing agent comprising metallic zinc and an alkali whereby the group represented by Y is removed and replaced with hydrogen, treating the product with an oxidizing agent and thereafter recovering 2-aminoe4-hydroxy-6-methylpyrimido [4,5-b] pyrazine.

No references cited. 

